This invention relates to a voltage regulator for a charging generator and more particularly, to a voltage regulator for a charging generator which is particularly suitable for use in a battery charging generator actuated by an automobile engine.
Voltage regulators for a charging generator regulate the output voltage of the charging generator and hold the voltage of a battery connected to the charging generator at a predetermined value. An example of such voltage regulator is disclosed in U.S. Pat. No. 3,718,849. In this device, an initial exciting current is caused to flow through the field coil of the generator from the battery through a charge lamp at the time of start by turning on a key switch. When the output voltage rises in accordance with the revolution of the generator, the exciting current is caused to directly flow from the output of the generator. For this reason, the charge lamp is lit at the initial excitation but is turned off when the output voltage of the generator rises. On the other hand, as the output voltage of the generator rises and the battery voltage also rises, the supply of the exciting current to the field coil is cut off. Accordingly, the exciting current attenuates and the output voltage of the generator drops. As the terminal voltage of the battery drops, the exciting current is again supplied to the field coil, raising the output voltage of the generator. A sequence of these operations are repeated to regulate the battery voltage to a constant voltage.
In the voltage regulator of the kind described above, the charging characteristics of the battery vary with temperatures so that the output voltage of the generator must be regulated in accordance with the temperatures. The voltage is controlled in such a fashion that the output voltage of the generator rises when the battery temperature is low and drops when the temperature is high.
In this instance, the relation between the voltage and an electric load to be connected to the battery must be taken into consideration. A current is ordinarily applied from the battery to the load such as a head light, various motors and the like of the automobile. If this impressed voltage is too high, the service life of the head light or the like is reduced and drop of the intensity of illumination of the head light, drop of the motor output and the like will occur.
It is therefore preferred to hold the voltage at a predetermined upper limit below a certain temperature and at a predetermined lower limit above a certain temperature and to regulate the voltage in match with optimum charging characteristics of the battery between these temperatures as disclosed in Japanese Patent Laid-Open Application No. 55-13629 (1980). In this case, a device having a simple circuit construction and yet making it possibe to set the characteristics must be realized.